1. Field of the Invention
The present invention relates to a gray level weighting centroid method, particularly to a gray level weighting centroid method for holographic data storage.
2. Description of the Related Art
The major optical storage system in the market is a CD-R machine, wherein the storage medium is CD or DVD. This kind of system focuses laser light on an optic disc through an object lens to bore holes, so as to program and record binary data on the optic disc. But the optic disc is only 2-D recording medium, the capacity of the optic disc is rather limited. Besides, the transmission speed of the optical storage system can't meet the demand required. Although the storage capacity of a hard disc drive is large, the data are transmitted to the hard disc drive in a point-to-point method. Therefore, the transmission speed of storage device has reached its limit and is not able to meet the requirement of transmission speed and storage capacity. However, holographic data storage technology has the advantage of high capacity and high access. Also, the recording medium for the holographic data storage technology is a 3-D recording medium, which transmits a whole page per unit time during transmission process. For example, the 1-TB data can be transmitted completely in around 8 seconds. Without doubt, the holographic data storage device is a promising product having high performance in the next generation.
The holographic data storage device has a strict requirement for optical quality and system adjustment. Since in high speed transmission, the holographic data storage device is affected by the noise such as aberration, thus the device is difficult to be a marketable product. Even if the product is existed, the price thereof is still very high, such as the holographic data storage product of Optware and Inphase Company. Refer to FIG. 1, the basic configuration of the holographic data storage device comprises a laser 10, a spatial filter 12, a first lens 14, a splitter 16, a spatial light modulator 18, a second lens 20, a storage medium 22, a third lens 24, a reflector 26, and a 2-D sensor 28. After the laser 10 emits a laser light, the laser light is passed through the spatial filter 12, the first lens 14, and the splitter 16 in sequence, and then the splitter 16 splits the laser light into a reference beam 30 and an object beam 32. Wherein the reference beam 30 moves toward the reflector 26, and the object beam moves toward the spatial light modulator 18. The reflector 26 reflects the reference beam to the storage medium 22. Besides, the spatial light modulator 18 can add the encoding code information to the object beam 32, and then the object beam 32 moves toward the storage medium 22. Finally, the object beam 32 interferes with the reference beam 30 to form a set of interference patterns, whereby the interference patterns are stored on the storage medium 22. Then, the object beam 32 is shielded, and the reference beam 30 left will read out the information from the storage medium 22. After the reference beam 30 is emitted into the storage medium 22, the diffraction light originated from the reference beam 30 is emitted onto the 2-D sensor 28. However, the aberration influence for the holographic data storage device can result in the distorted image received by the 2-D sensor 28.
In view of the problems and shortcomings of the prior art, the present invention provides a gray level weighting centroid method for holographic data storage, so as to solve the afore-mentioned problems of the prior art.